st: Imposing equality of means before permutation test

Dear Statalisters,
I am intended to resample an original dataset concerning observation of drug
A and drug B in terms of health care sector related costs since the original
sampling distribution of costs are heavily right-skewed.
A I have tried successfully to calculate the pbootstrap with the
non-parametric bootstrap approach following the procedure suggested by
Desgagné A, Anne-Marie Castilloux Am,1 Jean-François Angers JF, and LeLorier
J. The Use of the Bootstrap Statistical Method for the Pharmacoeconomic Cost
Analysis of Skewed Data. Pharmacoeconomics 1998 May; 13 (5 Pt 1): 487-497,
which requires to impose the equality of means to fulfil the t-test with
unequal variance precondition.
Now I would like to perform a Fisher's permutation test on the same dataset,
but I am not that sure that I have to impose the equality of means of costs
before running this latter test.
I does not seem so according to [R]Stata Manual release 9 and in Efron B,
Tibshirani RJ. An introduction to the bootstrap. New York: Chapman and Hall,
1993.
Any hints highly appreciated.
Thanks a lot for your kindness and for your time.
Kind Regards,
Carlo
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